The invention relates to an apparatus and method for providing brake control based on brake pedal travel and master cylinder pressure. In particular, the invention relates to an apparatus and method that blends a signal corresponding to brake pedal travel with a signal corresponding to master cylinder pressure in order to provide a brake control signal to a brake control loop.
Pressure control systems are necessary in order to control an amount of brake pressure to be applied and to be dumped from brake systems. Pressure control is used for electro-hydraulic brake (EHB) systems, which can also perform the control functions used for anti-lock brake systems (ABS), traction control systems (TC), and vehicle stability control systems (VSC).
A block diagram of a conventional braking system for a vehicle is shown in FIG. 1. Such a system is described in U.S. Pat. No. 5,551,769, issued to Mark Luckevich, and which is incorporated herein by reference. The conventional braking system is a hydraulic system, and includes a brake pedal 212, a brake switch 213, a brake master cylinder 214, control valves 216, brake fluid conduits 218, 220, 222, 224 and 226, as well as a right front wheel 228 and a left front wheel 230, and a pair of rear wheels 232.
The conventional system includes a pair of vehicle wheel speed sensors 234 for measuring the speed of each of the front wheels 228 and 230, and a pair of vehicle wheel speed sensors 236 for measuring the speed of each of the rear wheels 232. The system further includes a brake system control unit 238. Each of the wheel sensors 234 and 236 are operatively connected to the control unit 238, which is itself operatively connected to the anti-lock brake system control valve 216, via an electrical or fiber optic connection.
In conventional braking systems, such as that shown in FIG. 1, the driver input is through the brake pedal 212 to the master cylinder 214. This is a mechanical system in which the brake command and power is provided by the mechanical motion of a master cylinder piston acting on the brake fluid. The pressure is then boosted (usually with a vacuum system) and actuated through the fluid to the brake calipers and rotors.
In conventional braking systems, a brake signal based on an amount of travel of the brake pedal 212 is provided to the control unit 238. While this signal is useful in determining a desired amount of pressure to be applied at brake calipers, it is desired to have a signal that is more indicative of a desired amount of braking, as determined by activation of the brake pedal 212 by an operator of the vehicle.